Triazoles, especially benzotriazole and tolyltriazole, have found widespread application as corrosion inhibitors, chemical intermediates, catalysts and biocides. As corrosion inhibitors, triazoles are used in cooling water recirculating systems, antifreeze, rolling oils, cleaners, detergents, waxes, coatings, plastics and many other areas.
The level of triazole is especially critical in the cooling water usage. As industrial cooling water is lost due to evaporation, or when it is removed from the system to wash away sludge and deposits, additional fresh cooling water must be added to make up the amount lost. Since the level of triazole in the cooling water already in the system may differ from that being added along with the fresh cooling water, frequent monitoring is necessary to insure that the proper level of triazole is present in the system. In addition, once the triazole has been added to the system, the level may change due to plating out of the triazole onto the metal surfaces or possible reaction of triazole with contaminants in the aqueous system. Since it is important to maintain the concentration of triazole in the preferred range for corrosion inhibition, e.g. 1 to 10 parts per million, the cooling water must be frequently monitored to maintain the proper level of triazole. In a number of industries, this monitoring may be required on a daily basis.
Due to the importance of accurate measuring of the triazole concentration, several analytical methods for measuring this level have been proposed in the prior art. These methods include gas chromatography, spectrophotometry, liquid chromatography, potentiometry and various gravometric determinations. Discussions of these methods are presented in several literature sources including: Fagel, J. E., Jr., Ewing, G. W., Journal of the American Chemical Society, 73, (1951) 4360; Harrison, S., and Woodroffe, G. L., Analyst, 90, (1965) 44; Keil, R., Z. Anal. Chem., 71, (1971) 257; American National Standards Institute, ANSI PH 4, 204-1972; and Sherwin-Williams Company, Technical Bulletin 550, Revision B and other technical journals and publications.
All of the methods outlined in the prior art have several drawbacks. They are typically time consuming and they require skilled operators and relatively expensive analytical equipment which would not be conveniently located at the site of the cooling water. This invention overcomes the limitations of the prior art methods by providing an inexpensive and relatively rapid means of determining triazole concentration based upon a simple visual comparison. This invention provides a method which is convenient to use in the field at the site of the cooling water and does not require specially trained personnel to perform the test. This invention is capable of determining the level of triazole in concentrations of one part per million or less by a simple procedure which involves first a separation of the triazole from the aqueous solution and then a quantification based on the formation of a colored triazole complex.